1. Field of Invention
The current invention relates generally to apparatus, systems and methods for creating companders and inverse-companders. More particularly, the apparatus, systems and methods relate to a compander for OFDM signals. Specifically, the apparatus, systems and methods provide for companders based on an inverse square root (ISQR) function.
2. Description of Related Art
Orthogonal Frequency-Division Multiplexing (OFDM) is a multi-carrier communications signal modulation approach used in wireless communication standards that mitigates the primary problems associated with single-carrier, wide-band modulated signals. However, OFDM signals suffer from a critical problem. Due to the central limit theorem, an addition of many random signal components creates a Gaussian distributed signal, and thus a Rayleigh-distributed amplitude distribution. The long tail of the Rayleigh distribution gives rise to large outlier power values, thereby creating a large peak-to-average power ratio (PAPR). Several techniques have been developed to mitigate the PAPR problem, such as signal companding techniques. Recently, effective companders have been designed by piecewise modification of a signal amplitude distribution: a uniform component (UC) and a linear component (LC). Signal companders must be designed over the trade space of bit error rate performance, PAPR reduction, and out-of-band power rejection.